As integrated circuits become more complex, the circuit density of the chips increases. As this density increases, the thermal properties of a circuit package becomes a more important concern. The ability to remove heat generated from the high-powered and highly dense integrated circuits in a semi-conductor packaging becomes vital to the maintenance of the computer performance. The traditional method for cooling electrical devices has been through the use of air convection, a method operating on the idea of dissipating heat through the outer surfaces of the device and ultimately cooling it through the use of an airflow, usually driven by a fan. However, as the density and integration level of the integrated circuits along with the power requirements and the operating speed of the device all increase, the amount of heat dissipated by the system can no longer be adequately removed through the use of conventional air convection techniques. Even in cases where an adequate heat sink can be designed for removing the amount of dissipated heat, the physical size of this heat sink, which is of particular concern for compact devices such as laptop computers, becomes prohibitive.
The heat removal problem is further compounded by the geometry of the circuit board and its modules. Often an array of electronic modules are mounted on a flat printed circuit board. The modules may be of different shapes and geometry and therefore the height of a particular module can be much higher or lower than that of its neighbors.
Two problems occur with this kind of module configuration. First the module powers may be too high to be cooled by air cooling techniques along with other reasons described earlier. Therefore, the power levels dictate that liquid cooling should be used. Further, the second level packaging dictates a set of geometric constraints on the solution limiting the space available for cooling. In some cases, printed circuit cards plug radially into a horizontally located mother board. Thus, those components near the center of the second level package are afforded less space for cooling hardware than those at the outer radii. Light weight, low cost, material compatibility and no coolant leaks are other application requirements, especially when the preferred coolant is water.